Blood components separator disk

ABSTRACT

A separator disk for use in centrifugal separation of components is designed to automatically position itself during separation at the interface between the supernatant and the remaining components. Preferably the interface is between plasma and red blood cells.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/680,350 filed on Nov. 19, 2012, which is a continuation of U.S.application Ser. No. 12/453,577 filed on May 15, 2009, which is adivisional of U.S. application Ser. No. 11/206,869 filed Aug. 19, 2005,now U.S. Pat. No. 7,547,272, which is a divisional of U.S. applicationSer. No. 10/019,680 filed Jan. 4, 2002, now U.S. Pat. No. 7,077,273,which was the national stage of International Application No.PCT/US01/11732 filed Apr. 27, 2001, which was published in English, andclaims priority of U.S. Provisional Application No. 60/200,150 filedApr. 28, 2000.

This invention relates to methods and apparatus for use in theseparation of fluids into components having different specificgravities. The invention finds particular utility in the centrifugalseparation of the components of blood.

BACKGROUND

Centrifugal separation of blood into components of different specificgravities, such as red blood cells, white blood cells, platelets, andplasma is known from U.S. Pat. No. 5,707,331 (Wells). The apparatusshown in that patent employs a disposable processing tube having twochambers, and blood to be separated into components is placed in one ofthe chambers. The processing tube is placed in a centrifuge, whichsubjects the blood to centrifugal forces to separate the components. Thesupernatant is then automatically decanted into the second of thechambers.

To retain, principally, the red blood cells during the decant of thesupernatant, the apparatus disclosed in the Wells patent includes ashelf placed in the first chamber at the expected level of the interfacebetween the red blood cells and the less-dense components, including theplasma. One problem with the arrangement shown in the '331 Wells patent,however, is that the position of the interface varies with theparticular proportions of the components (e. g., the hematocrit) of theblood to be processed. Thus, if the shelf is placed at the expectedposition of the interface for blood of average hematocrit, and thehematocrit of the particular blood being processed is low, the shelfwill be above the interface after separation. Such a position of theshelf will hinder the flow of the components near the interface duringdecanting, thus retaining significant amounts of these components in thefirst chamber and reducing the separation efficiency of the system.

SUMMARY OF THE INVENTION

In accordance with the invention, a movable separator disk, whichautomatically positions itself at the interface between the separatedcomponents, is placed in the first chamber. In the preferred embodiment,the disk is capable of moving vertically and is designed to positionitself automatically at the interface between red blood cells and theremaining components in the centrifugal separation of blood.

Decant of the supernatant can be either by gravity drain or bycentrifugal transfer, and a main function of the disk is to restrict theflow of the component below it, e. g., red blood cells, during decant.This ensures that the supernatant is not contaminated and increases theefficiency of the process.

The invention contemplates two embodiments for the disk. In oneembodiment, the disk is supported on a central shaft such that anannulus is formed between the perimeter of the disk and the interiorsurface of the first chamber. The dimensions of the annulus are suchthat the flow of red blood cells through it during decant is restrictedsuch that they do not contaminate the decanted supernatant to anysignificant degree.

In another embodiment, the disk is arranged on the shaft such that, whenthe chamber is tilted for gravity decanting, the disk rotates such thatone edge of the disk engages the wall of the chamber to block flow ofred blood cells.

In either of these embodiments, the specific gravity of the disk and itsshape may be chosen so that a major part of the upper surface lies justbelow the interface, thus facilitating release of the supernatant fromthe disk during decanting. This upper surface is also preferably curvedto match the cylindrical shape the interface assumes duringcentrifugation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a longitudinal cross-section of a portion of a processingtube chamber and a separator disk in accordance with a first embodimentof the invention.

FIG. 1 b is a transverse cross section taken along line 1 b-1 b of FIG.1 a.

FIG. 2 a is a longitudinal cross-section of the embodiment of FIGS. 1 aand 1 b when the separator disk is tilted during decanting.

FIG. 2 b is a transverse cross section taken along line 2 b-2 b of FIG.2 a.

FIG. 3 a is a longitudinal cross-section of a second embodiment of theinvention.

FIG. 3 b is a transverse cross section taken along line 3 b-3 b of FIG.3 a.

FIG. 4 is a longitudinal cross-section of a third embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 and 2, one chamber 2 of a processing tube,such as that shown in the '331 Wells patent has a separator disk 4 inaccordance with the invention supported therein by a central shaft 6.The shaft 6 is designed to direct fluid introduced into the chamber tothe bottom of the chamber. This precludes the formation of an air bubbleat the bottom of the chamber, particularly when the bottom of thechamber is tapered. Thus, fluid is introduced into the chamber byinserting a cannula attached to a syringe containing blood into theshaft 6 and discharging the blood from the syringe into the chamber. Acentral opening 8 in the disk receives the shaft 6 in such a manner thatthe disk easily slides along the shaft.

The shaft 6 may not be necessary in all instances, for example, when thebottom of the processing tube is flat. In that instance the disk doesnot have a central hole.

The disk is preferably made of material having a specific gravity thatallows the disk to float at the interface with red blood cells. In thepreferred embodiment that specific gravity is about 1.04 (e. g.,polystyrene), which is just less than the specific gravity of red bloodcells at 70% hematocrit. Thus, when the blood is centrifuged, the diskmoves to the interface between the red blood cells and the othercomponents.

The interface will naturally assume a cylindrical shape with acylindrical radius equal to the distance to the center of rotation ofthe centrifuge. The disk may be cylindrical, to match the shape of theinterface.

In the embodiment shown in FIGS. 1 a, 1 b, 2 a and 2 b, the diameters ofthe hole 8 and the shaft 6 are such that an annular gap 10 is fannedbetween the outer surface of the shaft and the interior surface of thehole 8. Similarly, an annular gap 12 is provided between the perimeterof the disk and the interior surface of the tube 2.

FIGS. 1 a and 1 b illustrate the position of the disk duringcentrifugation, and it will be appreciated that the gaps 10 and 12 arelarge enough to allow passage of the descending heavier components, e.g., red blood cells and the ascending lighter components, e. g., plasma.According to this embodiment, however, the diameter of the centralopening 8 is large enough whereby during decanting the disk 4 rotates asshown in the figures.

Thus, when the processing tube is rotated to the decant position, themore dense red blood cells, illustrated at 14, that have accumulatedbelow the disk exert a force against the bottom of the disk as they tryto flow through the gap 12. This causes the disk 4 to rotate, as shownin FIGS. 2 a and 2 b, until a portion of the lower outer edge 16 of thedisk and also the upper outer edge 18 engage the inner surface of thechamber 2. This engagement between the edge 16 of the disk and theinterior of the chamber effectively forms a valve that prevents flow ofthe red blood cells, allowing decant of the plasma supernatant withoutcontamination by red blood cells. It will be appreciated that thisembodiment requires the transverse dimension of the disk between edges16 and 18 to be greater than the internal diameter of the tube so thatthe edges engage the interior of the tube when tilted.

A second embodiment is shown in FIGS. 3 a and 3 b. According to thisembodiment, the gap 10 is made to be small whereby the disk does notrotate appreciably during decant, in contrast to the embodiment of FIGS.1 and 2. It will be appreciated that an annular channel is formed by thegap 12, this channel having a width equal to the radial dimension of thegap and a length equal to the thickness of the disk at the edge. Therate of flow of a fluid through this channel is a function of thedimensions of the channel, and the dimensions of the disk of thisembodiment are such that the red blood cells will not flow appreciablythrough the channel at 1 G. In the preferred embodiment, the width ofthe gap is about 0.005 inch to about 0.020 inch, and the length is about0.1 inch to about 0.3 inch.

Thus, the components of the blood flow through the channel duringcentrifugation (i. e., at 1000 G), but do not flow appreciably throughthe channel during decanting at 1 G. This allows the supernatant to bedecanted without significant contamination by the red blood cells.

FIG. 4 illustrates a preferred shape of the disk 4. In this embodiment,the top surface 20 of the disk is concave, preferably cylindrical, andthe disk is provided with an elongated central portion 22. The specificgravity of the disk material is selected so that the concave surface 20is located just below the interface. That is, the thickness of the outeredge, the length of the portion 22, and the specific gravity of thematerial are chosen so that the center of buoyancy of the disk is justabove the concave surface, and that surface will be just below theinterface 26 with red blood cells. This arrangement allows a small layer24 of the red blood cells to form on the upper surface.

The layer of red blood cells 24 reduces the surface tension between theplatelets at the interface 26 and the surface 20 of the disk andfacilitates release of the platelets from the disk. This is important toensure that all of the platelets are decanted, and the small amount ofred blood cells that may be decanted along with the supernatant does notgenerally represent a significant contamination of the supernatant.

Modifications within the scope of the appended claims will be apparentto those of skill in the art.

We claim:
 1. In combination, a tube adapted to contain a fluid to besubjected to centrifugation and a separator disk in said tube adapted toseparate components of said fluid having different specific gravities,said disk being made of a material having a specific gravity near thespecific gravity of the components at an interface.
 2. A combinationaccording to claim 1 wherein said disk fits into said tube such that agap is formed between the perimeter of said disk and the interior ofsaid tube, said gap being of such a dimension that the component of saidbelow said disk after separation will not flow through said gap at about1G.
 3. A combination according to claim 1 further comprising a shaftextending along said tube and engaging said disk such that said diskslides along said shaft.
 4. A combination according to claim 1 whereinsaid disk is arranged to rotate about an axis transverse to thelongitudinal axis of said tube to form a valve with the side of saidtube during decanting.
 5. A combination according to claim 4 furthercomprising a shaft extending along said tube and engaging said disk suchthat said disk slides along said shaft.
 6. A combination according toclaim 4 wherein said disk includes an upper outer edge and a lower outeredge and the transverse dimension between said upper outer edge andlower outer edge is greater than the internal diameter of said tube. 7.A combination according to claim 1 wherein the upper surface is curved.8. A combination according to claim 7 wherein said upper surface iscylindrical.
 9. A combination according to claim 1 wherein said disk isshaped such that its center of buoyancy is located above an uppersurface of the disk.
 10. A combination according to claim 9 wherein thespecific gravity of said disk is such that its upper surface will liejust below an interface between plasma and red blood cells.
 11. Anarticle for use in preventing flow of a fluid from a tube, said articlebeing generally disk shaped and having a raised edge portion such thatthe center of buoyancy of the article lies above an upper surfacethereof.
 12. A method for decanting a supernatant that has beenseparated from a fluid comprising the step of placing a floatingseparator disk in said fluid, separating said supernatant from saidfluid, and decanting said supernatant wherein said separator diskautomatically positions itself at or near the interface between saidsupernatant and the remaining components of said fluid.
 13. A methodaccording to claim 12 wherein said disk is adapted to restrict decant ofsaid remaining components during decant of said supernatant.
 14. Amethod according to claim 13 wherein said disk rotates during decant toa position wherein at least one edge of said disk engages a wall of acontainer having said fluid therein.
 15. A method according to claim 13wherein said disk forms a channel between an outer edge of said disk andan interior wall of a container having said fluid therein, said channelrestricting flow of said remaining components during decant of saidsupernatant.
 16. A method according to claim 13 wherein said diskassumes a position such that its upper surface is just below aninterface between said supernatant and said remaining components.